1. Field of the Invention
The present invention relates to a multi-blade rotor for a windmill-type apparatus, including a hub supported on a shaft or fixed axle, and rotor blades that are connected to the hub, via bearing means, in such a way that the rotor blades are rotatable about their longitudinal axes.
2. Description of the Prior Art
In a windmill-type apparatus, in addition to wind stresses, cyclically acting forces and moments caused by the rotating rotor also occur. The stresses resulting from the rotation of the rotor are essentially alternating bending loads that are caused by the weight of the rotor blades and occur with each rotation of the rotor during the entire life expectancy; generally more than 1.times.10.sup.8 load reversals are produced. Since only relatively small stress amplitudes can be endured by the material due to breaks in the surface (threaded bores, holes, grooves, etc.), mold effects from casting and welded part contours, as well as irregularities in the material, the components (hub, rotor blade connection) subjected to such alternating bending loads must be very thick, and therefore have large masses, which is determinative for the dimensioning of the overall windmill-type apparatus, and stands in the way of the requirement for an optimum, economical construction.
It is therefore an object of the present invention to provide a multi-blade rotor of the aforementioned general type that has a hub which is easy to manufacture and which is characterized by a relatively low weight.